Very high density non-volatile memories utilizing Giant Magneto-Resistive (GMR) materials as the memory element integrated with CMOS devices or circuits have been proposed. These memories operate by storing information as the orientation of the magnetization vectors in the GMR memory elements. The magnetization vectors are oriented by means of applied magnetic (H) fields. The magnetic fields used to read and write the orientation of the magnetization vectors are generated by the integrated CMOS circuitry. Stray magnetic fields, generated external to the memory, having sufficient magnitude could cause errors in memory retention.
Stray or externally generated magnetic fields can come from an almost infinite number of sources. Stray magnetic fields having sufficient magnitude may cause the magnetization vectors stored in a magnetic memory to change uncontrollably. High density non-volatile magneto-resistive memories are especially sensitive to stray fields because the cells are becoming very small and, hence, require relatively low fields for reading and writing (switching or sensing the magnetic vectors). Also, stray fields from neighboring cells become larger as the distance between neighboring cells decreases at high densities.
One method of avoiding sensitivity to stray magnetic fields is to design the memory elements or cells such that they require higher switching fields than the stray fields they would encounter in commercial or military use. This method requires an exhaustive characterization of the stray fields encountered in these applications. This method also sets higher limits of internal power requirements to operate the memory, since higher internal fields requires more power to generate the higher internal fields, making them high power devices and, therefore, less desirable. The market for high density memories is extremely competitive. Cost differentials between suppliers of milli-cents per bit can mean success or failure in the market place. The addition of manufacturing steps or increased packaging complexity adds cost to the product which could determine the competitiveness of the product in the market place.
Accordingly it is highly desirable to provide a non-volatile magneto-resistive memory which is shielded from stray magnetic fields without adding substantial cost to the memory.
It is a purpose of the present invention to provide a new and improved non-volatile magneto-resistive memory with stray magnetic shielding.
It is another purpose of the present invention to provide a new and improved non-volatile magneto-resistive memory with stray magnetic shielding which does not add substantially to the cost of the memory.
It is still another purpose of the present invention to provide a new and improved non-volatile magneto-resistive memory with stray magnetic shielding which is incorporated into the standard passivation technique.
It is a further purpose of the present invention to provide a new and improved non-volatile magneto-resistive memory with stray magnetic shielding which also focuses the internally generated magnetic fields.
It is a still further purpose of the present invention to provide a new and improved non-volatile magneto-resistive memory with stray magnetic shielding which also focuses the internally generated magnetic fields so as to reduce the amount of power required to operate the memory.
It is a still further purpose of the present invention to provide a new and improved non-volatile magneto-resistive memory with focusing of the internally generated magnetic field.